1. Field of the Invention
This invention pertains to spherical pistons and particularly to high-pressure spherical pistons where the angular excursion of the piston as it rocks back and forth within the cylinder wall is a serious limitation in piston functioning
Previously, excessive rocking of spherical pistons caused metal to metal interference between the piston and the cylinder walls. To avoid this problem, the spherical diameter of the spherical piston is reduced past that recommended by piston o-ring standards to avoid metal to metal contact. As a result the diametral clearance is exceeded based on current standards. Lower pressure is now required to prevent o-ring extrusion. High pressure spherical pistons traditionally have required a spherical diameter greater than the diameter of the cylinder walls which contain the piston. As a result, spherical pistons have not been practical for high-pressure applications unless the angular excursion of the piston was limited to a very narrow range.
2. Description of the Prior Art.
Example of a prior art spherical piston application is set forth in U.S. Pat. No. 2,710,137. U.S. Pat. No. 2,710,137 is a classic example of the use of a spherical piston in the prior art. A spherical piston is resorted to because of a high angular excursion or rocking of the piston within the cylinder wall. In this particular example of a spherical piston, no o-ring is used which forces the piston to rely on lubrication to avoid friction problems due to metal to metal contact between the piston and the cylinder wall and to maintain a seal.
A refinement or variation of this type of rocking problem is shown in U.S. Pat. No. 2,792,790 where a spherical piston is used with an o-ring to attempt to avoid physical contact between the metal of the piston and the metal of the cylinder walls. The piston arrangement shown in U.S. Pat. No. 2,792,790 has the o-ring centered on the major diameter of the spherical piston and thus permits maximum pressure in both the compression and downward strokes. In this particular patent, however, the inventor states that the piston is designed to be cocked more while it is being withdrawn than during the compression stroke. This off-sets the matching pressure advantage of a normal push-pull piston.
U.S. Pat. No. 3,695,150 shows the various methods of o-ring seals that have been used previously in spherical or rocking piston assemblies. To avoid loss of pressure in such a rocking assembly, U.S. Pat. No. 3,695,150 as shown in FIG. 18 resorts to changing the cylinder walls such that they are not in the form of a true cylinder any more to maintain a high pressure seal.